Apparatus and method for analyzing, compressing or expanding speech and other sound recordings



Oct. 30, 1956 vlLBlG APPARATUS AND METHOD FOR ANALYZING,

0R EXPANDING SPEECH AND OTHER SOUND RECORDINGS Filed April 23, 1951 BYTZZZi I EN 1 3 m 9 9 S 9mm e e h I s E6 R P. M O C Oct. 30, 19562,769,031

F. VILBIG APPARA US AND METHOD FOR ANALYZING, COMPRESSING OR EXPANDINGSPEECH AND OTHER SOUND RECORDINGS Filed April 23. 1951 6 She ets-Sheet 2Oct. 30, 1956 F VlLBlG 2,769,031

APPARATUS ANDMEZTHOD FOR ANALYZING, COMPRESSING 7 OR EXPANDING SPEECHFiled April 25 1951 AND OTHER SOUND RECORDINGS 6 Sheets-Sheet 3 vINVENTOR. FE/EDE/Ch V/Lfi/ Oct. 30, 1956 F VlLBlG 2,769,031

APPARATUS AND METHOD FOR ANALYZING, CQMPRESSING OR EXPANDING SPEECH ANDOTHER SOUND RECORDINGS Filed April :25, 1951 6 Sheets-Sheet 4 v INFB/EDE/Lf/ JA 2 2 Wm, MD 64;:

Oct. 30, 1956 F VILBIG 2,769,031

APPARATUS AND METHOD FOR ANALYZING, COMPRESSING OR EXPANDING SPEECH ANDOTHER SOUND RECORDINGS Filed April 23. 1951' 6 Sheets-Sheet 5 EN 0R M4.

Oct. 30, 1956 F. VILBIG 2,769,031

APPARATUS AND METHOD. FOR ANALYZING, COMPRESSING 0R EXPANDING SPEECH ANDOTHER SOUND RECORDINGS Filed April 25. 1951 6 Sheets-Sheet 6 orroe/vevsAPPARATUS AND METHOD FOR ANALYZING,

COMPRESSING OR EXPANDING SPEECH AND OTHER SOUND RECORDINGS The inventiondescribed herein may be manufactured and used by or for 'the Governmentfor governmental purposes without payment to me of any royalty there- Itis known from the work of J. F. Schouten (Philips Technische Rundschau,vol. 10, pgs. 310317 and Octooer 1939 pgs. 302-303, also vol. 3, pg.310, 1938) that a tone film strip produced by the Philips-Miller method,when illuminated from a point source of light, dilfracts the light afterthe manner of a Rowland grating. The present inventor makes use of thiseflect for the purpose of producing an apparatus for speech compressionand expansion and for speech analysis. In speech band compression orexpansion, all of the frequencies of the band are divided or multipliedin a certain ratio without changing the time dimension. Other recordedsounds may be treated similarly.

There are numerous practical uses for a sound analysis apparatus capableof compressing or expanding speech or other sound. If a sound frequencycan be divided, say into quarters, so that a frequency can be obtainedwhich is one-fourth the frequency of the original sound, this lowerfrequency can be transmitted by radio or by a loud speaker and when sotransmitted it'can be understood through much heavier interference thanthe original sound. By this process, it is also possible to understandthe transmission of a friendly radio station despite enemy efforts tojam it. The apparatus and method to be described herein will also beuseful in visually analyzing the voices of singers to make their defectsapparent to them and also to analyze and then improve the acousticqualities of musical instruments and loud speakers.

It is the object therefore of this invention to provide a method andapparatus which will be useful in attaining the goals which have abovebeen discussed.

Referring to the accompanying drawings:

Fig. 1 is a more or less diagrammatic representation of a knife which iscutting a sound track through the emulsion coating of a sound filmaccording to the Philips- 5 Miller method. The means for vibrating theknife according to the modulations of the sound waves is not shownbecause it is well known. j I

Fig. 2 shows schematically an apparatus for producing an oscillographicrepresentation or analysis of a filmsoun'd track made according'to thePhilips-Miller method.

Fig. 3 is a photographic reproduction of asourid track, above, and belowthe diffraction pattern thereof produced by the apparatus shown in Fig.2. v V i V Fig. 4 is a plan view ofa hand-drawn frequency multiplicationand division.

Fig. 5 is a diagrammatic representation of an apparatus employing thedisc shown'in 'Fig. 4 for the purpose of frequency multiplication anddivision, for example to reduce the frequency of the sound track whichhasv been recorded upon a sound film. I

Fig. 6 is a diagrammatic representation of an disc suitable for 65apparatus nite States Patent 'fication and the claims.

for making a pattern disc which is useful in the frequencymultiplication and division of sound.

Fig. 7 is a plan view of an improved disc produced by the apparatusshown in Fig. 6. It has the same purpose of the disc shown in Fig. 4. v

Referring again to Fig. 1, it) is a triangular knife which is held bymeans not shown, in light contact with a sound film it. The knife 16 isprovided with a chisel edge 12 which is quite sharp and which whenvibrated by a modulating means (not shown) is able to remove theblackened emulsion of the sound film into a track 13 of varying area inaccordance with the sound pressure variation of the sound beingrecorded. The steps described comprise the Philips-Miller method and arethe steps referred to whenever the term Philips-Miller method is used inthespeci- It is a characteristic of this Philips-Miller method of soundrecording that the track obtained is bounded on each side by a Wavewhich is more or less sinusoidal according to the number and order ofhigher harmonics in the original sound. Each sinusoidal wave opposes itsneighbor. It is also true that each cut varies in thickness from itsneighbors thereby giving a prismatic effect.

Referring to Fig. 2, 14 is a roll upon which a sound film 11 madeaccording to the Philips-Miller method is wound. This film is beingwound from the roll 14 onto the other roll 15 by power means, not shown,if desired. The Philips-Miller track may be made by the knife 10 shownin this apparatus from fresh film wound on the roll 14 so that theanalysis of the track 13 wiil take place almost immediately after it isrecorded. 16 is a brilliant point light source, the ray formations fromwhich are sent through a small condensing lens 17 and thence through asmall hole 18 in a screen 19 at the focus of the lens 17. The light rays20 are next directed onto a larger planoconvex lens 21 which directs therays 20 in parallel bundles 22 through the track 13 which produces adiffracted bundel of rays 22. This bundle is then received in alano-convex lens 23, so that the optical spectrum produced by thediffracting action of thesound track is focused upon a screen 24 inwhich there is a vertical slit 25. From the work of Schouten it is knownthat this spectrum will take the form of one of those in- Fig; 3, inwhich each of the frequencies present in the sound track will bedisplayed on either side of a center line as vertical lines of light,their spacing'from center being proportional to frequency and theirintensity in proportion to their am' plitude. There will also be avariation in height due to the variable height of the sound track usedas a diffraction grid. By means of the vertical sl-it 25 it is possibleto eliminate the variable height portions extending beyond the edges ofthe slit. By positioning the slit so that one end is atthe-center line,it will pass only one-half of the double spectrum, while the other halfis arrested by the screen 24. It is immaterial which half of thespectrum is transmitted through the slit. The image in the slit is thenthrown in enlarged form by the action of lens 26 and prism 27 ontoscreen 32. A rotating prism 27 is inter- V posed between lens 26 andscreen 32, causing the spectral lines thrown upon the screen to rotatein circular paths about thecenter, the innermost circles correspondingto the lower frequencies and the outermost to the higher frequencies.The prism 27 may be rotated at a regulatable speed by a belt'28 or otherdriving mechanism which is ner the spectral lines of the low frequencieswill cross the spiral first and the high frequencies last. The screen 32does not ordinarily rotate but for some applications, which will laterbe discussed, rotating means may be provided. Behind the screen 32 thereis a plane-convex lens 35 mounted with its plane side in close up towardthe screen. Its diameter is at least equal to that of the spiral slot33. Whenever a spectral line crosses the spiral the light from thespiral will be focused by lens 35 onto the sensitive area of photocell36 and converted by it into voltage pulses which are transmitted byleads 37 and 38 to 'an amplifier 39, the output of which is takenthrough leads 40 and 41 to the vertical deflecting electrodes of akinescope 42. The horizontal deflecting electrodes are fed with a sawtooth wave by oscillator 43, which is synchronized with the motor 29which drives the prism. The frequency in cycles per second of the sawtooth wave is therefore the same as the number of revolutions per secondof the rotating prism. Each saw tooth is originated by means, not shown,at the instant the spectral lines are in a position opposite the originof the spiral slot, so that the electron beam of the kinescope willsweep across its face in synchronism with the rotation of the spectrallines about their centers. The horizontal position of the cathode ray atany instant will then be in proportion to the angular position of thespectral lines at that instant.

When a spectral line crosses the spiral the cathode ray will bedeflected vertically by the voltage pulse forming a vertical pip 44. Thehorizontal position of the pip will depend on its frequency, the lowerfrequency pips being formed on the left side of the screen if the sweepgoes from left to right. This is because the low frequency spectrallines will cross the spiral first. The amplitude of the vertical pipswill be in proportion to the amplitude of the frequency component whichit represents, since the brighter spectral lines will cause thephotocell to deliver larger pulses to the vertical deflecting plates.For convenient use as an analyzer the face of the kinescope may becalibrated horizontally in terms of frequency and vertically in terms ofamplitude.

Discussing the operation of the apparatus shown in Fig. 2, it is to benoted that the sound film may be used immediately after being scrapedwith the knife edge 12 with a delay time of less than second. If aphotographic film is moved across the slot'25, the continuous soundspectrum of the first film can be written upon the second one. But onlythe position of the single frequencies and only inelfectively, theamplitudes can be indicated by the greater or lesser blackness of thelines. If it is desired to produce immedately a picture of thefrequencies present and their amplitudes, a lens 26 must be placedbehind the slot. This lens gives an amplified picture on the screen ofthe spectral lines passing through the small slot 25. If the rotatingprism 27 is employed behind the lens, the spectral points are projectedon the screen 32 in circular paths. The circles having a small radiuscorrespond to the low frequencies and those of large radius to thehigher frequencies. The spectral slot 33 is a true Archimedean spiral.The light can pass the slot 33 if the light point circle cuts thespiral. At this moment the light which passes the spiral slot will becondensed by the condenser lens 35 onto the photo-cathode of thephotocell 36 to produce the photo current impulse. The impulse isapplied to the vertical deflection plates of the cathode ray tube orkinescope 42 after amplification. A

- linear saw tooth voltage is'applied to the horizontal plates.

division and multiplication if instead of the spirally slotted screen, atransparent modulation or pattern disc 52, which is shown in Fig. 4, isemployed. This disc 52 is made of a sheet of transparent material onwhich is drawn a series of concentric circles 52a, each circleconsisting of alternate clear and darkened areas as in Fig. 4. The rateof alternation increases regularly toward the periphery. The coordinatebackground of Fig. 4 illustrates the relationship. If light from aspectral line corresponding to a frequency component present in thesound track falls on a given circle, the light passing through the discwill be modulated as it passes over the alternate light and dark areasof its circular path. This arrangement is illustrated in Fig. 5. Therate of modulation will be dependent on the R. P. S. of the prism and onthe number of sets of alternate dark and transparent areas in thecircular path. For example, a sound frequency of 300 cycles can be madeto produce a spectral light point which rotates in a small circle.

Now if this circular path falls on a circle having 10 sets of alternatedark and light areas and if the prism rotates at 6 R. P. S., then afrequency 60 C. P. S. will be produced in the output of the photocell36. If the R. P. S. is changed to 60, then a frequency of 600 C. P. S.will be produced. Because the pattern or modulation disc can be changedin any manner, it is also possible to produce any division ormultiplication ratio thereof. For example, it is possible to diminishthe low frequency by factor of 3 and slowly to increase the compression.This is advantageous because of the transient time of speech.

It has been mentioned that it is possible to divide a speech frequencyby a factor, for example 3. The output of amplifier 39 (Fig. 5) couldthen be transmitted by radio or wire and would be less subject tointerference because the noise is proportional to the band width intransmission and by sending a reduced band width, a corresponding amountof noise can be filtered off. Such a reduced frequency, aftertransmission and reception could be sent through the apparatus shown inFig. 5, in which the rotation of the prism 27 for example is speeded up300% or alternatively, if the prism stands still, the disc 52 is rotatedthree times faster than the prism originally rotated. The originalfrequency of the speech would be thereby restored.

The pattern disc shown in Fig. 4 is not entirely satisfactory becausethe abrupt changes in the black and white areas will produce square waveimpulses containing many harmonics. Sinusoidal light modulation is moredesirable and is preferred. A light modulation disc similar to thoseshown in Fig. 7 can be produced by using the apparatus shown in Fig. 6.Referring to Fig. 6, 50 is an opaque movable plate having a very finehole through it. If this hole (not shown) is illuminated through a tube51 with a parallel beam of monochromatic light, the beam will makecircles on a disc (photographic plate) 52 when the prism 27 is rotated.'If the plate 50 with the hole is moved slowly in a radical direction, aspiral appears on the photographic plate. If the ascendency on thespiral line is very slow so that spiral lines touch each other, thephotographic plate will be uniformly black (following development). Forproduction of the light pattern, the light which illuminates the holemust be modulated sinusoidally with slowly increasing frequency. Thismay be done with3a polarized light and a rotating analyzer 53. For theproduction of the slowly increasing light modulation frequency, a smallfriction wheel 54 is provided and moved across a constantly rotatingdisc 55 which is driven by an electric motor 56. One revolution of thedisc 55 will be necessary for the purpose of preparing one sinusoidallymodulated spiral turn on the pattern disc 52. The rotating analyzer 53is driven by means of a belt 57 by the small wheel 58 which is connectedto the wheel 54 equal diameter by means of a shaft 59. Since the eX-posure time of the light falling upon the disc 52 decreases with theradius, the light intensity must be regulated by means of a slowlymoving absorption glass 60. Both the plate 50 and the adsorbing glass 60are driven from the shaft 61 of the electric motor 56. The shaft 61enters a gear box 62 containing a reduction gear (not shown) whichimparts to an extension shaft 63 a slower number of R. P. M. than thespeed of the shaft 61. Mounted on the shaft 63 are pulleys 64, 65 and 66each at a higher level than the preceding. The glass 60 is driven fromthe pulley 65 and is attached to a fixed base by a spring 67. The plate50 is driven from the pulley 66 and is attached to a fixed base by aspring 68. The small wheel 54- is moved outwardly from the center of thedisc 55 by a cord 69 which is wound over the pulley 64 and tightlyattached thereto.

The light which is used in the tube 51 is derived from a monochromaticpoint source 70 and is condensed by a condensing lens 71, the focalpoint of which is located at a distance beyond the far side of theabsorbing glass 60. By means of lens '73 the light is caused to passthrough the polarizing disc 74 and thence through a rotating analyzer 53thereby modulating the light sinusoidally. Then there will appear on thepattern plate 52 the sinusoidally modulated pattern or disc shown inFig. 7.

From the foregoing description, it is evident that a new method of radiocommunication has been described in which a transcription is firstprepared of the radio message which is to be sent. This transcription ismade a reduced frequency which is considerably lower than the frequencywhich would ordinarily be transmitted. The frequency should be at least/3 lower, but is preferably /2 or even 4 lower than would be customarilytransmitted and also lower by a like proportion to the interferencewhich the radio transmission is likely to encounter. That is to say,that if an enemy jamming transmitter is operating on a frequency of1,000 C. P. S., the message to be transmitted should first be preparedby transcription to a frequency of from 666 C. P. S. to 250 C. P. S. Themessage is then transmitted without altering the total length of timethat it would have taken to transmit the message before the frequencywas reduced. The reduced frequency message is then received, recordedand its frequency multiplied by the same factor as was used in reducingits frequency before transmission, or as near thereto as feasible. Theapparatus necessary to make the reduction and multiplication offrequency is not necessarily the apparatus which has been disclosed.Other apparatus, operating upon different principles, for example theprinciple of heterodyning, acoustic or electrical, can be employed solong as the total time base remains unaltered. This process oftransmitting intelligence by radio is specifically claimed in mydivisional application filed June 22, 1953, bearing the Serial Numbe!363,422.

The invention claimed is:

1. Means for analyzing sound waves recorded on a film as a variable areasound track comprising means for illuminating the film with a pointsource of light to form a line spectrum of light representing componentsound frequencies of the illuminated zone of the sound track, means forforming a rotating optical image of the line spectrum, means having aspiral slot for line scanning the rotating spectral image, a photocellfor receiving the light transmitted through the scanning means andproducing an electrical pulse output representative of the frequencycomponents of the area of the sound track being illuminated.

2. An apparatus for the visible analysis of speech recorded upon tonefilm in strip form, by vibrating a chiseledged knife in contact withblackened sound film to remove blackened emulsion therefrom when theknife is being vibrated by a modulating means to produce a tone trackbounded on its sides by wavy lines, which includes a source of light,means for arranging light from said source in parallel bundles of rays,means for transilluminating said film and the tone track thereon withthe bundle of parallel light rays, a lens for receiving and condensingthe diffracted light which has passed the tone track, a first screenhaving a slit arranged at the focal point of said lens to pass the lightfrom only one side of said tone track, lens means for amplifying theimage which passes said first screen, a prism positioned to receive thelight passed by the amplifying lens means, a variable speed electricmotor for rotating said prism whereby to convert the prism receivedlight into a succession of circles, at least two conductors supplyingsaid motor with electric current, a second screen in which there is anArchimedean spiral slot positioned to intercept the concentric circlesof light produced by rotation of the prism, a condensing lens positionedbehind the second screen to receive the light passed through said slot,a photocell positioned at the focus of said last-mentioned condensinglens to generate electrical pulses from the light pulses received, anelectrical amplifier for said electrical pulses, a kinescope of thecathode ray tube type having a pair of electrostatic plates to receivesaid impulses and a second pair of electrostatic plates at right anglesthereto, a sawtooth wave-generating oscillator energized from theconductors supplying the electric motor, said sawtooth wave beingapplied to said second pair of electrostatic plates, whereby said pulseswill be rendered visible in a form similar to spectroscopicpresentation.

3. Means for altering the frequency of a succession of sounds recordedon film as a variable area sound track comprising means for illuminatingan area of the film with a point source of light to form a line lightspectrum representing the component sound frequencies of the illuminatedzone of the sound track, means for rotating an image of the linespectrum at a constant predetermined speed, a filter adapted to passlight from said rotating spectrum image, said filter having concentricfilter bands, each band having alternate transparent and opaque sectorssuch as to pulse the light received from the rotating spectrum image bya desired factor and photoelectric means for converting the light pulsesinto electrical pulses of the desired altered frequency.

References Cited in the file of this patent UNITED STATES PATENTS2,312,835 Hansell Mar. 2, 1943 2,403,983 Koenig July 16, 1946 2,403,986Lacy July 16, 1946 2,439,392 Jones Apr. 13, 1948 2,521,954 Tuttle Sept.21, 1950

